Surgical implant and surgical fixing screw

ABSTRACT

A surgical implant ( 2 ) for fusing adjacent vertebrae (V) together comprises a body portion ( 4 ) with spaced arms ( 10 ). The body portion ( 4 ) has passages ( 16   a  and  16   b ) to receive surgical fixing screws ( 100 ) engaged in holes drilled in the vertebrae (V) for securing the body portion ( 4 ) to the anterior faces of the vertebrae (V) to be fused. The arms ( 10 ) extend into a prepared space between the vertebrae to be fused. Graft material is packed between the arms ( 10 ). Each surgical fixing screw ( 100 ) has an externally screw-threaded shank ( 101 ) divided into wings which can be outwardly deformed to anchor the shank ( 101 ) in the hole. Each surgical fixing screw ( 100 ) also had a head ( 102 ) which can be transformed between a laterally expanded condition and a laterally contracted condition to permit the head to be interlocked with the implant ( 2 ).

The present invention relates, in a first aspect, to a surgical implantfor use with a bone graft between vertebrae, more particularly cervicalvertebrae, in order to fuse said vertebrae, to a system comprising saidimplant and to a method of facilitating the fusion of adjacent vertebraeusing said system.

The present invention also relates, in a second aspect, to a surgicalfixing screw which may be used for surgical applications generally, butwhich is particularly suitable for use with the surgical implantaccording to the first aspect of the invention.

With regard to said first aspect of the present invention, in certainspinal disorders, such as degenerative disease of the intervertebralsubstance (hereinafter simply referred to as “disc”), it is necessaryfor the disc to be removed and the neighbouring vertebrae to be fused,aided by a bone graft inserted between the vertebrae. Inevitably, thefusion process is slow, and it is desirable for the bone graft andvertebrae to be immobilised for fusion to take place with the vertebraeand graft correctly positioned.

One solution (exemplified by the so-called Cervical Spine Locking PlateSystem, available from Synthes) is to insert the bone graft between thevertebrae and then secure the vertebrae to each other by means of ametal plate which lies along one face (generally the anterior face) ofthe vertebrae. The plate is held in place against the vertebrae byfixing screws which pass through holes provided in the plate and whichare screwed into holes drilled into the vertebrae. The bone graft ismaintained in position by compressive forces. In use, however, such aplate can be difficult to align properly.

In another system (Fournitures Hospitalieres) a metal plate isintegrally formed with a metal ring which protrudes perpendicularly fromthe midpoint of the plate. The plate can be supplied with a disc ofhydroxy-apatite bone substitute fixed in the region enclosed by thering. The ring containing the hydroxy-apatite disc is inserted betweenthe vertebrae which presents the metal plate in the correct alignmentfor securing to the vertebrae by means of fixing screws. Alternatively,the plate is supplied without the disc of hydroxy-apatite and thesurgeon prepares the bone graft. Difficulties arise if it is necessaryto remove the plate, since the entire bone graft will also be removed,requiring the whole procedure to be repeated.

The latter system is not suitable for fusing three adjacent vertebrae.

It is an object of the first aspect of the present invention to providea surgical implant which facilitates the fusion of adjacent cervicalvertebrae, and obviates or mitigates the abovementioned problems.

According to said first aspect of the present invention, there isprovided a surgical implant comprising:

(i) a body portion having first and second passages therethrough, saidpassages being adapted and disposed in said body portion so as to becapable of receiving a securing element (e.g. a screw) for securing saidimplant to first and second adjacent vertebrae (eg cervical vertebrae)respectively; and

(ii) first and second mutually spaced arms carried by and extending awayfrom said body portion;

wherein said arms are adapted so as to be capable of insertion betweensaid first and second adjacent vertebrae, and wherein at least part ofsaid body portion is adapted to engage with anterior faces of bothadjacent vertebrae when said arms are located between said adjacentvertebrae, so that, in use, a bone graft can be held in position betweenthe first and second arms and between mutually facing superior andinferior surfaces of said first and second adjacent vertebrae.

Preferably, the body portion of the implant is constructed such thatwhen the arms of the implant are located between said first and secondadjacent vertebrae, another implant can be secured to the anterior faceof one of the first and second adjacent vertebrae and a third vertebra,said third vertebra being adjacent to the same one of said first orsecond adjacent vertebrae.

The arms are preferably straight and preferably also mutually parallel.

Preferably, upper and lower surfaces of each arm are roughened and/orprovided with a hydroxy-apatite coating. In use, said surfaces will bein contact with the facing superior and inferior surfaces of theadjacent vertebrae. The roughened surface and/or hydroxy-apatite coatingencourages in-growth of bone, thereby providing additional securement ofthe implant.

The body portion may be provided with more than two passages. Mostpreferably three or four passages are provided. At least one passagepreferably has its axis inclined to the arms. More preferably, at leastsaid first and said second passages have mutually inclined axes.

Preferably, the implant is of a unitary construction of biocompatiblematerial. Examples of suitable materials include titanium, titaniumalloy and stainless steel.

Also according to said first aspect of the present invention, there isprovided a system for fusing adjacent vertebrae (eg cervical vertebrae),said system comprising at least one surgical implant in accordance withsaid first aspect, at least one bone graft and securing elements forsecuring the implant to adjacent vertebrae.

Also according to said first aspect of the present invention, there isprovided a method of fusing adjacent vertebrae (eg cervical vertebrae)comprising the steps of:

(i) introducing bone graft material between first and second adjacentvertebrae,

(ii) locating the arms of a surgical implant in accordance with saidfirst aspect around said bone graft material and between said adjacentvertebrae,

(iii) securing at least one securing element into the first vertebra,and

(iv) securing at least one securing element into the second vertebra,wherein each securing element passes through a respective one of saidpassages in the body portion of the implant.

The method may be extended to the fusion of a third vertebra, said thirdvertebra being adjacent to one of said first and second adjacentvertebrae, in which case the above steps are repeated with respect tothe first and third vertebrae or the second and third vertebrae usinganother surgical implant.

Preferably, said securing elements are fixing screws of which at leastone may be a surgical fixing screw according to said second aspect ofthe present invention.

With regard to said second aspect of the present invention, it is anobjection to provide a design of surgical fixing screw which enables asecure fixing of a part such as an implant to take place with a reducedrisk of disengagement from such part.

According to said second aspect of the present invention, there isprovided a surgical fixing screw including a head and a screw-threadedshank, wherein the head is formed so that it can be transformed betweena laterally expanded condition and a laterally contracted condition.

The term “laterally” means laterally relative to the longitudinal axisof the shank. Preferably, the head is formed so that it can betransformed between a radially expanded condition and a radiallycontracted condition.

Preferably, the surgical fixing screw further includes retaining meansengageable within the head for preventing the head from beingtransformed into its laterally contracted condition.

When in its laterally contracted condition, the surgical fixing screwcan be inserted within an aperture in the part to be secured. When inits outwardly extended condition, the head of the surgical fixing screwenables fixing of the screw within the aperture in the part in a mannersuch as to reduce the risk of disengagement of the surgical fixing screwfrom the part.

In a preferred embodiment, the head is shaped so that, in its laterallyexpanded condition, it projects laterally into an undercut recess in thepart whereby the head is prevented from disengagement from the part byinterlocking with the latter.

Preferably, the head of the surgical fixing screw has a recess thereinin which the retaining means is engageable so that the retaining meansengages a wall of the recess to prevent the head from being transformedinto its laterally compressed condition.

Also according to said second aspect of the invention, there is provideda surgical fixing screw comprising a head and an externallyscrew-threaded shank which is divided longitudinally into lateral wingswhich are capable of being deformed outwardly of the longitudinal axisof the shank. This obviates or mitigates the risk of the screw becomingdetached from, or loosened in, a hole in bone or hard tissue in whichthe screw shank is engaged in use.

Conveniently, the shank is adapted to receive an expansion means which,during insertion into the fixing screw, causes the outward deformationof the wings. Desirably, the body of the shank tapers inwardly away fromthe head.

Preferably, the expansion means is held within the shank by means of acomplementary thread arrangement.

Most preferably, the expansion means for causing outward deformation ofthe wings and the retaining means for the head are provided as differentparts of a single retaining and expansion element engageable with theshank and the head of the screw.

Preferably, the surgical fixing screw is constructed and adapted for usein the securing of a surgical implant in position.

The head of the screw may have a first formation for engagement, in use,by a screwdriver and a second formation, spatially distinct from thefirst formation, for engagement, in use, by an alternative screwdriver.Thus, in the event that one of the first and second formations becomesdamaged during insertion or removal of the screw using the appropriatescrewdriver, the screw can be removed subsequently using the otherscrewdriver on the other of the first and second formations.

Desirably, said first and second formations are spaced apartlongitudinally in the axis of rotation of the surgical fixing screw.

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a surgical implant in accordance withsaid first aspect of the present invention;

FIG. 2 is a plan view of the surgical implant shown in FIG. 1;

FIG. 3 is an end-on view of the surgical implant shown in FIG. 1;

FIG. 4 is a cross-sectional view of the surgical implant shown in FIG.1;

FIG. 5 is a schematic illustration showing the attachment of twosurgical implants according to the present invention to a singlecervical vertebra;

FIG. 6 is a side view of an example of a surgical fixing screw accordingto said second aspect of the present invention;

FIG. 7 is a axial section through the surgical fixing screw of FIG. 6;

FIG. 8 is a perspective view of the surgical fixing screw of FIGS. 6 and7;

FIG. 9 is an end view of the head of the surgical fixing screw of FIGS.6 to 8;

FIG. 10 is a side view of an expansion element for use in the fixingscrew of FIGS. 6 to 9;

FIG. 11 is a plan view similar to FIG. 2 of another embodiment ofsurgical implant;

FIG. 12 is a side view of the implant of FIG. 11;

FIG. 13 is an axial section through an embodiment of surgical fixingscrew for use with the implant of FIGS. 11 and 12;

FIG. 14 is a perspective view of the surgical fixing screw of FIG. 13;

FIG. 15 is an axial section showing the surgical fixing screw of FIGS.13 and 14 with an inserted retaining and expansion element;

FIG. 16 is a detail showing the interengagement between the screw ofFIG. 15 and the implant of FIGS. 11 and 12; and

FIG. 17 is a view showing the use of the implant of FIGS. 11 and 12 andsurgical fixing screws of FIGS. 13 to 15 to secure two cervicalvertebrae together.

Referring to FIGS. 1 and 2, the surgical implant 2 is U-shaped andcomprises a curved flange-like body portion 4 having a posterior majorsurface 6 a, an anterior major surface 6 b, a superior edge surface 8 aand an inferior edge surface 8 b, and a pair of mutually spaced,parallel straight arms 10. The implant 2 is of unitary construction and,in this embodiment, is made from titanium alloy (complying with BS7252PT3 1990). At each opposite lateral end region of the body portion 4, arespective one of the arm 10 extends away from the body portion 4. Thedepth of the arms 10 (i.e. the distance between their upper surfaces 12a and lower surfaces 12 b) is less than that of the body portion 4, suchthat upper end abutment surfaces 14 a and lower end abutment surfaces 14b are defined on the body portion 4. The superior and inferior surfaces12 a, 12 b of each arm 10 are roughened and provided with ahydroxy-apatite coating (not shown). The body portion 4 is provided withtwo pairs of identical passages 16 a and 16 b which extend through thebody portion 4 from the posterior major surface 6 a to the anteriormajor surface 6 b of the body portion 4.

Referring to FIGS. 3 and 4, the passages 16 a are spaced apart along thebody portion 4 at a distance from the superior edge surface 8 a of thebody portion 4, while the passages 16 b are at the same distance fromthe inferior edge surface 8 b of the body portion 4 and offset relativeto the first passages 16 a. Each passage 16 a, 16 b comprises anteriorand posterior coaxial cylindrical regions 18 a, 18 b of differentdiameters such that an annular step 20, which serves as a seat for afixing screw, is defined at their intersection. The axis of each of thepassages 16 a is inclined above the direction of extent of the arms 10by 10°. The axis of each of the passages 16 b is inclined below thedirection of extent of the arms 10 by 10°.

The surgical implant 2 may be used in an operation where, for whateverreason, it is necessary to replace the intervertebral disc between apair of adjacent cervical vertebrae by a bone graft. In such anoperation, the disc (or fragments thereof) is removed and the inferiorsurface of a first (superior) disc and the superior surface of anadjacent second (inferior) disc are prepared for the reception of a bonegraft. Bone graft material is compacted between the vertebrae and thearms 10 of the implant 2 are pushed between the vertebrae, either sideof the bone graft material, from the anterior side of the vertebrae. Therespective regions of the posterior major surface 6 a abut the anteriorsurfaces of the first and second vertebra.

The fact that the arms 10 of the implant 2 are located between thevertebrae ensures that there is no error in the alignment of the implant2 before it is fixed in place. Such fixing is achieved by forming holesin the vertebrae using the passages 16 in the body portion 4 as guides,followed by inserting expanding surgical fixing screws, for examplesurgical fixing screws 100 as described below, through each passage 16a, 16 b in the body portion 4 and into the respective vertebra.

In cases where two or more consecutive discs must be removed, it ispossible to repeat the above procedure relative to one of the first andsecond vertebrae and a superior or inferior adjacent third vertebrausing a second implant, and so on. It should be noted that the offsetpositioning of the passages 16 a, 16 b ensures that the screws used tofix the respective first and second implants do not interfere with eachother. This is illustrated in FIG. 5, where it can be seen that thedesign of the implant is such that two identical implants 2 a and 2 bcan be secured to a single vertebra V using the two intermediate pairsof screws 100 which are mutually offset because of the positioning ofthe passages 16 a, 16 b. It will be understood that the vertebrae (notshown in FIG. 5) which are adjacent to the illustrated vertebra V willbe respectively secured by upper and lower pairs of screws 100illustrated in FIG. 5.

Each surgical fixing screw 100 is tightened until the head of the screwis seated against the annular step 20, at which point the vertebrae aresecurely fixed relative to each other. The fixing in place of theimplant 2 is enhanced by the inclination of the passages 16 in the bodyportion 4, which makes it more difficult for the implant 2 to work loosethan if the passages 16 a, 16 b were mutually parallel or parallel tothe direction of extent of the arms 10. The expanding nature of thescrews 100 also assists in ensuring a secure fixing of the implant inplace. Once in place, the roughened and hydroxy-apatite coated superiorand inferior surfaces 12 a, 12 b encourage in-growth of bone on thosesurfaces 12 a, 12 b of the arms 10 only.

In the above-described procedure, it is generally intended for theimplant 2 to remain permanently in place, however, there may becircumstances in which it is necessary for it to be removed. Should thisbe necessary, the implant 2 can be withdrawn by unscrewing the screws100 and withdrawing the implant. Clearly, any bonding between the upperand lower surfaces 12 a, 12 b of the arms with the vertebrae must bebroken, but the bone graft between the arms 10 will remain intact. Thus,replacement or permanent removal of the implant 2 can be achievedwithout requiring a second bone graft.

Referring now to FIGS. 6 to 9, the surgical fixing screw 100 comprisestwo parts, a shank 101 and a head 102. The shank 101 has an exteriorscrew thread 103 such that the body of the shank 101 decreases indiameter away from the head 102. The flight 104 of the screw thread 103is, however, of constant diameter over the region AB, decreasing indiameter in only the terminal turn adjacent A. The flight 104 has a flatcrest which increases in width towards the head 102 over the region AB.A passage 105 extends longitudinally throughout the length of the fixingscrew 100. Two diametrically opposed slots 106 extend radially inwardlyfrom the peripheral surface of the shank 101 to communicate with thepassage 105. The slots 106 and passage 105 extend over the length of theshank 101 so as to divide the latter longitudinally into two lateralwings 107.

The passage 105 comprises three parts, a tapered end region 108, anintermediate screw-threaded region 109 and a head end region 120. Thehead end region 120 defines an internal recessed hexagonal formation 121which opens onto the head end of the screw 100 and which, in use,engagingly receives a screwdriver having a hexagonal bit (not shown).

A step 122 is defined at the junction between the regions 109 and 120which are situated within the head 102 of the screw 100. The step 122faces the head end of the screw and has a cross-recessed formation 123therein which, in use, engagingly receives another screwdriver having across-headed bit (not shown). It will therefore be understood that theformations 121 and 123 are spatially distinct (in this embodiment, theyare spaced apart along the longitudinal axis of the screw) and areindependently engageable by the respective screwdrivers.

The screw-threaded region 109 is adapted to receive an expansion element124 (FIG. 10) which will be described later.

The tapered end region 108 of the passage 105 tapers inwardly away fromthe intermediate screw-threaded region 109 and extends over the whole ofthe length of the shank 101.

The head 102 has an outer peripheral surface 126 provided with a radiallip 127 so as to form an abutment shoulder 128 for engagement, in use,against the step 20 described above.

Referring now to FIG. 10, the expansion element 124 comprises a headregion 130, an intermediate externally screw-threaded region 131 and arod-like region 132. The head region 130 has a slot 133 for cooperativeengagement by a further screwdriver bit. The intermediate screw-threadedregion 131 is engageable with the internal screw-threaded region 109such that the expansion element 124 can be fixed within the passage 105.The rod-like region 132 projects from the threaded region 131 and has adiameter larger than the minimum diameter of the tapered region 108.

In order to effect engagement of the fixing screw 100 in bone, aborehole is drilled in the latter and the screw 100 is secured in theborehole by rotating it using the hexagonal or cross-recessed formations121 or 123 with the appropriate screwdriver. Then, the expansion element124 is inserted into the screw 100 and is rotated using the furtherscrewdriver bit engaged in the slot 133.

When the expansion element 124 is fully engaged within the passage 105,the action of the rod-like region 132 upon the internal surfaces of thetapered region 108 of the passage 105 deforms the lateral wings 107outwardly, thus locking the screw 100 in the borehole and inhibitingbacking out or loosening of the fixing screw 100.

If necessary, the fixing screw 100 can be extracted from the bone, afterremoval of the expansion element 124, by use of a suitable screw driverengaged with either of the formations 121, 123. This allows the optionof choosing one specific formation 121 or 123 should the alternativeformation 123 or 121 become damaged or otherwise unserviceable. Thischoice is especially advantageous as the lateral wings 107 will remaindeformed after the removal of the expansion member 124 and therefore aneffective engagement of the screwdriver with the chosen formation isessential.

The above described surgical fixing screw 100 may be used for othersurgical applications.

Referring now to FIGS. 11 and 12, the surgical implant 2 is, like thatof FIGS. 1 to 5, for fusing adjacent cervical vertebrae together, andsimilar parts are accorded the same reference numerals. In thisembodiment, however, the arms 10 are not disposed at opposite lateralends of curved flange-like body portion 4 but are spaced slightlyinwardly of the ends. Also, as can be seen from FIG. 12, the superiorand inferior surfaces of the arms 10 are not mutually parallel but aremutually tapered. This tapering is chosen so as to restore and/ormaintain cervical lordosis (natural curvature of the spine). The lateralsurfaces of the arms 10 are, however, mutually parallel as in the caseof the embodiment of FIGS. 1 to 4.

A variety of implants 2 of different size may be provided with the arms10 available in varying heights and widths to fit different anatomies.

Notches 17 are provided in the ends (lateral faces) of the body portion4 and on the free ends (posterior faces) of the arms 10. These notches17 enable the surgeon to tie a suture around the implant in order tohold the bone graft in position during insertion.

As can best be seen from FIG. 17, the superior and inferior faces of thebody portion 4 are formed with complementary recesses and lugs to enableadjacent implants to be stacked closely together. In this embodiment,the implant 2 has two superior apertures 16 a and one inferior aperture16 b.

Referring now to FIGS. 13 to 15, surgical fixing screw 100 is similar tothat of FIGS. 6 to 10 and similar parts are accorded the same referencenumerals. In this embodiment, however, head 102 has a series of fourequi-angularly spaced slots 140 extending from the outside of the head102 to open into the head end region 120 of the passage 105. These slots140 permit the head to be transformed between a laterally relativelyexpanded condition as illustrated in FIGS. 14, 15 and 16 and a laterallyrelatively contracted condition (not shown). These slots 140 also enablea screwdriver with a cross-headed bit to be engaged with the head 102 ofthe screw 100. Internal recessed hexagonal formation 121, in thisembodiment, is disposed within the region of the shank 101 adjacent thehead 102 rather than within the latter.

In this embodiment, the passage 105 does not extend over the full lengthof the shank 101 but terminates at a conical end wall spaced from thefree end of the shank. The slots 106 extend over part of the lengthportion 108 of the passage 105 to the free end of the shank 101. Also,the portion 108 of the passage 105 is not tapered but is parallel sided.

The head region 130 of the expansion element 124 comprises an inwardlytapering frustoconical head portion 130 a and a cylindrical head portion130 b. The frustum of the head portion 130 a has a larger diameter thanthe adjacent head portion 130 b so that a step 130 c is defined betweenthese two portions. The head portion 130 b is of a size such that it isrotatable with clearance within the hexagonal formation 121. The base ofthe frusto-conical head portion 130 a is equal in diameter to that ofthe head end region 120 of the passage 105 when the head is in itslaterally expanded condition.

Referring now to FIG. 16, the surgical fixing screw 100 described abovein relation to FIGS. 13 to 15 is mainly intended to be used with thesurgical implant described above in relation to FIGS. 11 and 12.However, it does have other potential surgical uses. The anterior region18 a of each passage 16 a or 16 b has a diameter which is slightly lessthan that of the radial lip 127. Adjacent to the anterior region 18 a ofthe passage 16, there is an undercut annular recess 150 following whichthe posterior region 18 b of the passage 16 is provided. The posteriorregion 18 b has a diameter which is marginally greater than the outerdiameter of the head 102 of the screw 100.

In order to secure the implant 2 in position, a hole is drilled into therespective cervical vertebra through each aperture 16 a, 16 b. Then,each fixing screw 100 is inserted through the respective aperture 16 aor 16 b and rotated to cause it to advance into the hole in the cervicalvertebra until the lip 127 engages against the body portion 4 around theanterior end of the passage 16. Because the lip 127 is curved, the head102 is deformed radially inwardly into its laterally contractedcondition as permitted by the partial closure of the slots 140. Thisallows the lip 127 to pass through the anterior region 18 a and into therecess 150. When it reaches the recess 150, the head 102 is free tospring outwardly so that the lip 127 extends into the recess 150,thereby providing an interlock to prevent unwanted disengagement of thelip 127 from the undercut recess 150. The screw 100 can then be fullytightened to urge the implant against the cervical vertebrae. Then, theexpansion element 124 is inserted into the screw 100 and rotated so asto cause the wings of the screw to be expanded outwardly to anchor thescrew within the hole drilled in the cervical vertebra. At the sametime, the head region 130 of the expansion element 124 enters the recess120 fully and serves to retain the head 102 against being compressedradially inwardly. The head portion 130 a may also serve to urge thehead portion 102 outwardly if any permanent deformation of the head ofthe screw has taken place as a result of the lip 127 being forcedthrough the smaller diameter anterior region 18 a of the passage 16. Inthis way, the screw 100 is securely interlocked with the body portion 4of the surgical implant 2.

FIG. 17 shows the arrangement where three screws 100 are used to securethe surgical implant 2 in position, with two of the screws being engagedwith the upper cervical vertebra V and one screw being engaged with thelower cervical vertebra V of the pair to be fused together. The superiorand inferior faces of the body portion 4 of the implant 2 are suitablyshaped with a lug and recess arrangement to enable each portion 4 to benested closely with the body portion(s) 4 of adjacent implant(s) 2.

What is claimed is:
 1. A surgical implant comprising: a body portion having first and second passages therethrough, each of said passages being adapted and disposed in said body portion so as to be capable of receiving a securing element for securing said implant to first and second adjacent vertebrae respectively; and first and second mutually spaced arms carried by and extending away from said body portion; wherein said arms are adapted so as to be capable of insertion between said first and second adjacent vertebrae, and wherein said body portion comprises profiled surfaces for engagement with corresponding anterior faces of both adjacent vertebrae when said arms are located between said adjacent vertebrae, so that, in use, a bone graft can be held in position between the first and second arms and between mutually facing superior and inferior surfaces of said first and second adjacent vertebrae.
 2. A surgical implant as claimed in claim 1, wherein the body portion is constructed such that, when the arms are located between said first and second adjacent vertebrae, another implant can be secured to the anterior face of one of the first and second adjacent vertebrae and a third vertebrae, said third vertebrae being adjacent to the same one of said first or second adjacent vertebrae.
 3. A surgical implant as claimed in claim 1, wherein the arms are straight and mutually parallel.
 4. A surgical implant as claimed in claim 3, the arms having superior and inferior surfaces for engaging corresponding surfaces of said adjacent vertebrae, wherein the arms between said superior and inferior surfaces are mutually tapered away from said body portion.
 5. A surgical implant as claimed in claim 1, wherein the body portion is provided with more than two passages.
 6. A surgical implant as claimed in claim 5, wherein said first and second passages are axially off-set relative to each other.
 7. A surgical implant as claimed in claim 1, wherein at least one passage has its axis inclined to the arms.
 8. A surgical implant as claimed in claim 1, wherein at least said first and said second passages have mutually inclined axes.
 9. A surgical implant as claimed in claim 1, wherein at least one of said passages has an undercut recess therein.
 10. A surgical implant as claimed in claim 1, wherein at least one of said passages comprises a portion for interlocking with an expandable portion of said securing element so as to prevent disengagement thereof.
 11. A system for fusing adjacent vertebrae comprising: at least one surgical implant having: a body portion having first and second passages therethrough, each of said passages being adapted and disposed in said body portion so as to be capable of receiving a securing element for securing said implant to first and second adjacent vertebrae respectively; and first and second mutually spaced arms carried by and extending away from said body portion; wherein said arms are adapted so as to be capable of insertion between said first and second adjacent vertebrae, and wherein said body portion comprises profiled surfaces for engagement with corresponding anterior faces of both adjacent vertebrae when said arms are located between said adjacent vertebrae; at least one bone graft for insertion between the first and second arms and between mutually facing superior and inferior surfaces of said first and second adjacent vertebrae; and securing elements for securing the implant to said first and second adjacent vertebrae so that, in use, said bone graft can be held in position.
 12. A method of fusing adjacent vertebrae comprising the steps of: introducing bone graft material between first and second adjacent vertebrae, providing a surgical implant comprising: a body portion having first and second passages therethrough, each of said passages being adapted and disposed in said body portion so as to be capable of receiving a securing element for securing said implant to first and second adjacent vertebrae respectively; and first and second mutually spaced arms carried by and extending away from said body portion; wherein said arms are adapted so as to be capable of insertion between said first and second adjacent vertebrae, and wherein said body portion comprises profiled surfaces for engagement with corresponding anterior faces of both adjacent vertebrae when said arms are located between said adjacent vertebrae, locating the arms of said surgical implant around said bone graft material and between said adjacent vertebrae, securing at least one securing element into the first vertebra, and securing at least one securing element into the second vertebra, wherein each securing element passes through a respective one of said passages in the body portion of the implant.
 13. A surgical implant comprising: a body portion having first and second passages therethrough, each of said passages being adapted and disposed in said body portion so as to be capable of receiving a securing element for securing said implant to first and second adjacent vertebrae respectively; and first and second mutually spaced arms carried by and extending away from said body portion; wherein said arms are adapted so as to be capable of insertion between said first and second adjacent vertebrae, and wherein at least part of said body portion is adapted to engage with anterior faces of both adjacent vertebrae when said arms are located between said adjacent vertebrae, so that, in use, a bone graft can be held in position between the first and second arms and between mutually facing superior and inferior surfaces of said first and second adjacent vertebrae and wherein said arms extend from said body portion so as not to enclose said bone graft so that said implant can be removed leaving said bone graft intact.
 14. A surgical implant as claimed in claim 13, wherein the body portion is constructed such that, when the arms are located between said first and second adjacent vertebrae, another implant can be secured to the anterior face of one of the first and second adjacent vertebrae and a third vertebra, said third vertebra being adjacent to the same one of said first or second adjacent vertebrae.
 15. A surgical implant as claimed in claim 13, wherein the arms are straight and mutually parallel.
 16. A surgical implant as claimed in claim 15, the arms having superior and inferior surfaces for engaging corresponding surfaces of said adjacent vertebrae, wherein the arms between said superior and inferior surfaces are mutually tapered away from said body portion.
 17. A surgical implant as claimed in claim 13, wherein the body portion is provided with more than two passages.
 18. A surgical implant as claimed in claim 17, wherein said first and second passages are axially off-set relative to each other.
 19. A surgical implant as claimed in claim 13, wherein at least one passage has its axis inclined to the arms.
 20. A surgical implant as claimed in claim 13, wherein at least said first and said second passages have mutually inclined axes.
 21. A surgical implant as claimed in claim 13, wherein at least one of said passages has an undercut recess therein.
 22. A surgical implant as claimed in claim 13, wherein at least one of said passages comprises a portion for interlocking with an expandable portion of said securing element so as to prevent disengagement thereof. 